(A) Field of the Invention
The present invention is related to a dish antenna, and more specifically, to an adjustment method for a dish antenna.
(B) Description of Related Art
A satellite television system employs a dish antenna to collect satellite signals, and the signals are then reflected to low noise block down converters (LNB) equipped at the focus of the dish antenna for amplifying the signals and reducing their frequencies down to around 1 GHz, i.e., the radio signals are transformed to an intermediate frequency. The adjusted signals are transmitted via a cable to an indoor television channel selector for selecting the signals of a desired channel, and the selected signals are then amplified, modulated and converted into video and audio signals for television viewing.
A dish antenna is a highly directional receiving device, which has to be precisely directed toward satellites in orbit at 36,000 kilometers altitude. For example, if a dish antenna with a 180 cm diameter shifts 2 cm horizontally, or 3 cm vertically, the signals will become weak or even disappear. In addition, if a dish antenna uses the Ka band, i.e., 26-40 GHz, an adjustment accuracy of 0.1 degrees is needed, and the tolerance has to be within 0.02 degrees for aiming at satellites precisely.
Normally, a dish antenna using the Ka band is adjusted by using a programmable logic controller (PLC) in control of servo motors; however, the high cost significantly limits its popularity.
FIG. 1 illustrates a known adjustable antenna apparatus 1 including a dish antenna 10, an LNB 11, a support rod 12, an adjustable dish bracket 13 and an adjustable base member 14. When the adjustable antenna apparatus 1 is disposed in different manners by securing the adjustable base member 14 at different places such as a vertical wall surface or a horizontal or inclined roof, the adjustable dish bracket 13 is used for adjusting the orientation of the dish antenna 10 to obtain optimal signal-reception performance. However, the adjustable dish bracket 13 only roughly adjusts the angle or fixing position of the dish antenna 10 according to the scale thereof, and obviously the dish antenna 10 cannot be fine-tuned within a precision smaller than the scale. In other words, the dish antenna 10 cannot be easily adjusted to an optimal angle or a fixing position.
Moreover, the dish antenna 10 is fixed after being adjusted, and there is no need for further adjustment. Accordingly, the adjusting mechanism is used only one time and is not cost-effective.